1. Field of the Invention
The present invention relates to a motor driving device for a vacuum pump, and a vacuum pump having the motor driving device.
2. Description of the Related Art
Axial vacuum pumps such as turbo molecular pumps rotate rotors having a rotor blade at a high-speed for evacuation. At this time, since exhaust is carried out while rarefied gas is being compressed, the rotors move only in one direction (this rotational direction is positive rotation). Therefore, the axial vacuum pumps normally accelerate and decelerate between a stationary state and a positive rotation region, and steadily rotate in the positive rotation.
Conventionally, as information necessary for motor driving for rotating rotors, rotational speed information and magnetic pole positional information about motor rotors are obtained based on detection signals of rotation sensors. For example, in a vacuum pump that detects targets (having gaps) provided to rotors by inductance type gap sensors, it is difficult to detect the rotational direction using only the rotation sensors. For this reason, normally, the above problem is handled by devising a control sequence in the motor driving (particularly, at a start time when reverse rotation likely occurs) (for example, see JP 4692891 B).
However, when the rotation of the rotors is started from the stationary state (activated), the reverse rotation occasionally occurs at an excitation start time, and the control sequence is devised, but instead the activating time is lengthened.
Further, when an axial vacuum pump such as a turbo molecular pump is mounted to a large vacuum chamber and the chamber is quickly returned from the vacuum state to an atmospheric pressure state, the atmospheric pressure state is gained while gas is counter-flowing from a pump side to a chamber side. For this reason, a rotor infrequently rotates in a reverse manner due to a function of gaseous regurgitation. In such a case, in order to prevent activation in the reversely rotating state, the pump should wait for starting of reactivation between the reversely rotating state and stationary state of the rotor.